This invention relates to a process and apparatus for piecing a yarn at a spinning unit of an open-end friction spinning machine. Such spinning units have two friction rollers that are drivable in the same rotational direction and are arranged next to one another to form a wedge-shaped gap. A feeding and opening device is provided for the feeding of single fibers, via a fiber-feeding channel, to the wedge-shaped gap. A yarn withdrawal device is provided for drawing off the formed yarn in the longitudinal direction of the wedge-shaped gap, and a suction device is provided for holding the forming yarn in the wedge-shaped gap. For the joining or piecing of the yarn, an already spun end of the yarn is returned and fed to the wedge-shaped gap, and the previously interrupted feeding of the individual fibers is resumed and the yarn is drawn off.
A piecing process for a spinning unit of an open-end friction spinning machine is known that must be carried out manually from European Published Unexamined Application (EP-OS) No. 34 427, where a yarn end is cut into a length in such a way that it reaches up to the feeding point of the fibers, and is then, via a yarn withdrawal tube, returned into the closed spinning unit. Special measures are taken at the spinning unit with the objective of holding the yarn in a stretched position and first bringing it into a position located at a distance to the wedge-shaped gap from where it is then to be transferred to the wedge-shaped gap in the stretched position. In the case of this design, the yarn end is essentially returned on the circumference of the roller that rotates into the wedge-shaped gap and is not interrupted in its drive. Then the fiber feeding device is turned on. Subsequently, the yarn withdrawal is resumed. The known process is difficult to carry out and offers no control as to whether the yarn end really arrives in the area of the feeding point since one cannot look into the wedge-shaped gap so that there is no possibility of control. There is also the danger that the yarn end moving on the roller rotating into the wedge-shaped gap takes up an uncontrolled position. It does not seem possible to produce even yarn piecing sections with this system that have such a high quality that they can remain in the yarn and do not interfere with further processing of the yarn.
The invention is based on the objective of providing a process and apparatus of the initially mentioned type by means of which it is possible to return the yarn end in a controlled manner for a yarn piecing process and to actually bring the yarn end into the area where the feeding of the fibers takes place.
This objective is achieved according to the invention by exposing the wedge-shaped gap, before the return of the yarn end, by moving away a lid-shaped component containing at least one part of the fiber feeding channel, by subsequently inserting the yarn end onto the mouth of the fiber feeding channel of the lid-shaped component, by then returning the lid-shaped component into its position covering the wedge-shaped gap, after which the actual piecing process takes place by switching on the yarn withdrawal device and the fiber feeding device and transferring the end of the yarn end to the wedge-shaped gap.
In a controlled manner, the yarn end is therefore, before the actual piecing process, returned in such a way that it is securely located in the area of the feeding point, namely in the area of the mouth of the fiber feeding channel. Since the spinning unit is opened for this purpose, a control of the return of the yarn end is possible without difficulty. The necessary work is simple to carry out so that, in particular, automatically operating machines may also be used. Because of the face that the yarn end comes to be located in the fiber feeding channel, it moves, when it is drawn off again, in the same direction as the refed fibers so that, together with the fibers, it reaches a position that is favorable with respect to piecing.
In an advantageous development of the invention, it is provided that the introduction of the yarn end into the fiber feeding channel of the lid-shaped component is supported by an air current directed at the yarn end and into the fiber feeding channel. As a result, the yarn end, in a simple manner, can be brought into the desired position while it is stretched simultaneously.
It is advantageously provided that, after the closing of the lid-type component, the yarn end is continuously returned. This ensures that the actual end of the yarn end reaches the area of the fiber feeding point, i.e., of the mouth of the fiber feeding channel, only after a certain time period after the yarn withdrawal device is turned on again, so that sufficient time is available for the individual steps of the piecing process. In this case, it is especially advantageous when the path covered by the end of the yarn end during rewithdrawal is monitored and that the passing of the end of the yarn end at one point is used as a signal for carrying out other operating steps of the piecing process. This makes it possible to exactly coordinate those individual operating steps with respect to time that must be carried out when the end of the yarn end passes the fiber feeding point.
In an advantageous development of the invention, it is provided that the drive of the rollers is interrupted during the return of the yarn end until the rewithdrawal of the yarn and/or the switching-on of the fiber feeding device. This ensures that the yarn end is not overwound or overtwisted by the rollers, which could reduce the quality of the yarn in the area of the yarn piecing section.
In an advantageous development according to the invention, it is provided that the yarn end is held at a distance to the wedge-shaped gap and is transferred to the wedge-shaped gap only after the fiber feeding device is turned on. Especially when the end of the yarn end was previously worked into a type of tuft or fiberbeard, there is the advantage that the end of the yarn end comes in contact with the already approaching flying fibers in the fiber feeding channel and moves in the same rotational direction with the fibers in the wedge-shaped gap so that qualitatively an especially good yarn piecing section can be obtained.
In a further development of the invention, a device for carrying out the process is provided where the spinning units, in each case, have a lid-shaped component that can be moved between an operating position covering the wedge-shaped gap and an open position exposing the wedge-shaped gap and that contains the mouth of the fiber feeding channel that is exposed in the open position. Because of this development, it is possible to return a yarn end in a simple manner for the piecing process and to position it in such a way that it is located at a point that is appropriate for spinning, i.e., at the feeding point, namely the mouth of the fiber feeding duct.
In a further development of the invention, a device is provided for the opening and closing of a spinning unit requiring maintenance, by moving away the lid-type component, and a device for the return of one yarn end which, in the open position, can be delivered to the mouth of the fiber feeding channel of the lid-type component. In this manner, the return of the yarn end can be automated.
In an advantageous development of the invention, it is provided that the device for the return of the yarn end into the fiber feeding duct of the lid-type component contains at least one blowing nozzle aimed into the fiber feeding channel. This facilitates the return of the yarn end and also achieves that this yarn end is stretched in the fiber feeding channel.
In a further development of the invention, a device for the switching-on of the fiber feeding mechanism is provided, permitting a coordination of the feeding with the piecing process.
In an especially advantageous development of the invention, a maintenance unit is provided that can be moved along the open-end friction spinning machine and contains the device for the opening and closing of the lid-type component, the device for the return and the rewithdrawal of the yarn end and the device for the switching-on of the fiber feeding mechanism. This results in the advantage that the devices carrying out the piecing process must only exist once. Another advantage is that by means of these devices, the same working motions are carried out for each piecing process in the same time-coordinated sequence. It is also possible to carry out the working sequences, especially the rewithdrawal of the yarn end and the switching-on of the fiber feeding mechanisms, at speeds that are suitable for spinning.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.